This invention relates to an improved valve member or element, particularly, though not exclusively, for use in a fluid flow passage in a hydraulic door closer for controlling fluid flow past an associated valve seat therein.
U.S. Pat. No. 4,148,111 discloses a hydraulic door closer in which in a flow return passage thereof is disposed a valve member which cooperates with a valve seat to control the damping effect of the hydraulic fluid as the door closes under the influence of the closer return spring. The valve member is adjustable towards and away from its associated valve seat to vary the rate of fluid flow past said seat.
Moreover to compensate for changes in the temperature of the hydraulic fluid, which can result in its `thickening` or `thinning`, i.e. an increase or decrease in its viscosity, the valve member is formed as a first portion of relatively dimensionally stable material, and a second portion of material of greater coefficient of thermal expansion. The first portion is typically of metallic material, such as steel, as it is exteriorly screw-threaded for engagement with a complementary interior screw-thread of the flow return passage, whilst the second portion is typically of plastics material such as nylon. The two portions are an interference fit together to provide, in effect, a one-piece composite valve member. With similar types of thermo-compensating valve elements, the two portions are insert molded together, to form the one-piece composite valve member.
One disadvantage of these known one-piece composite valve members is that they are each specifically for use with a particular form of flow passage and valve seat, so that little, if any, inter-changeability of elements is possible. A further more general disadvantage of this type of restrictor/regulator valve member, whether of integral or of composite one-piece form, is the possibility that when it is screw-threadedly engaged in the flow passage, vibration/temperature/pressure can cause it to move angularly in its associated interior screw-thread formed in the passage, and thus self-adjust. This changes the closing time characteristic of the closer and thus necessitates more frequent maintenance of the door closer than would otherwise be necessary.
The foregoing illustrates limitations known to exist in present one-piece composite valve members. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.